Zinc Coordination‐Polymer‐Mediated Self‐Assembly of Nanoparticles into “Brick‐and‐Mortar” Membranes for Hydrogen Separation

Zeolitic imidazolate framework‐8 (ZIF‐8) with high stability and porosity is a promising candidate for hydrogen separation membranes. However, most ZIF‐8 polycrystalline membranes exhibit low H2/CO2 (kinetic diameters of 2.9/3.3 Å) mixed gas selectivity, due to the intercrystalline defects and the unprecise molecular sieving originated from framework flexibility of ZIF‐8 structure with a theoretical aperture size of 3.4 Å. Here, inspired by nacre’s “brick‐and‐mortar” structure, we develop mixed matrix type composite membranes in which dominant crystalline ZIF‐8 nanoparticles (bricks) are interconnected by ultrathin zinc coordination polymer interlayers (mortar) via self‐assembling. Driven by coordination bonds between Zn2+ from precursor colloid and branched polyethyleneimine (PEI), a zinc coordination polymer network is formed to connect ZIF‐8 nanoparticles through interactions between Zn2+ of coordination polymer and surface terminal groups on ZIF‐8 nanoparticles, thus eliminating intercrystalline void defects and providing a highly selective H2 transport pathway. Meanwhile, the micropores and large cavities in ZIF‐8 allow fast H2 transport. Benefitting from both highly selective pathway and fast H2 transport through porous ZIF‐8, the optimized ZIF‐8‐PEI membrane exhibits a record‐high H2 permeability of ~1.78×105 Barrer with a high mixed gas H2/CO2 selectivity of 176, surpassing state‐of‐the‐art performance. This bioinspired multifunctional membrane expands the scope of molecular sieving membrane.